A combined high-performance liquid chromatographic-microbiological assay for serum folic acid

Abstract

An assay of folic acid in human serum is described involving HPLC fractionation of deproteinized serum prior to Lactobacillus casei assay. High specific activity [3H]folic acid is added as internal standard to 1 ml serum prior to deproteinization with perchlorate and an aliquot is applied to a C18 reverse-phase HPLC column. The folic acid fraction was assayed by L. casei microtiter plate assay. Intra- and interassay variations (CV) were 5.5 and 7.5% respectively for sera (n = 10) spiked with folic acid. The percentage recovery for folic acid additions of 10 and 20 ng/liter were 105.2 and 103.7%, respectively. The lower limit of detection was 1 ng folic acid/ml serum. Folates other than folic acid and 5-methyltetrahydrofolate were not detected. The assay permitted serial measurements to be made of folates in serum following an oral dose.